Connected: An Internet Encyclopedia
RFC 792 - Information Request or Information Reply Message

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### Information Request or Information Reply Message

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |      Code     |          Checksum             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Identifier          |        Sequence Number        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       IP Fields:

       Addresses

          The address of the source in a information request message will be
          the destination of the information reply message.  To form a
          information reply message, the source and destination addresses
          are simply reversed, the type code changed to 16, and the checksum
          recomputed.

       IP Fields:

       Type

          15 for information request message;

          16 for information reply message.

       Code

          0

       Checksum

          The checksum is the 16-bit ones's complement of the one's
          complement sum of the ICMP message starting with the ICMP Type.
          For computing the checksum , the checksum field should be zero.
          This checksum may be replaced in the future.

       Identifier

          If code = 0, an identifier to aid in matching request and replies,
          may be zero.

       Sequence Number

          If code = 0, a sequence number to aid in matching request and
          replies, may be zero.

       Description

          This message may be sent with the source network in the IP header
          source and destination address fields zero (which means "this"
          network).  The replying IP module should send the reply with the
          addresses fully specified.  This message is a way for a host to
          find out the number of the network it is on.

          The identifier and sequence number may be used by the echo sender
          to aid in matching the replies with the requests.  For example,
          the identifier might be used like a port in TCP or UDP to identify
          a session, and the sequence number might be incremented on each
          request sent.  The destination returns these same values in the
          reply.

          Code 0 may be received from a gateway or a host.

Next: Summary of Message Types

Connected: An Internet Encyclopedia
RFC 792 - Information Request or Information Reply Message